2008-01-09 Jan Kratochvil <jan.kratochvil@redhat.com>
Support attaching to stopped processes/threads and/or with pending
signals. This ChangeLog entry is OBSOLETE:
* linux-nat.c (STRINGIFY, STRINGIFY_ARG): New macros.
(kill_lwp): New declaration.
(linux_ptrace_post_attach, pid_is_stopped): New function.
(linux_child_follow_fork): New comment about WAS_STOPPED.
(lin_lwp_attach_lwp): Variable PID removed. Part replaced by a call to
LINUX_PTRACE_POST_ATTACH.
(linux_nat_attach): Likewise.
(linux_nat_detach): Optionally stop the detached process.
(linux_nat_resume): Clear WAS_STOPPED if appropriate.
* NEWS: Document the new behaviour.
2007-06-30 Jan Kratochvil <jan.kratochvil@redhat.com>
* gdb.texinfo (Attach): Document the ATTACH and DETACH commands for
stopped processes. Document the messages on the seen pending signals.
2008-02-24 Jan Kratochvil <jan.kratochvil@redhat.com>
Port to GDB-6.8pre.
Index: gdb-6.8cvs20080219/gdb/NEWS
===================================================================
--- gdb-6.8cvs20080219.orig/gdb/NEWS 2008-02-24 19:35:37.000000000 +0100
+++ gdb-6.8cvs20080219/gdb/NEWS 2008-02-24 19:36:26.000000000 +0100
@@ -412,6 +412,9 @@ Renesas M32C/M16C m32c-elf
Morpho Technologies ms1 ms1-elf
+* On GNU/Linux, stopped processes may get attached to now. Signals being
+delivered at the time of the attach command no longer get lost.
+
* New commands
init-if-undefined Initialize a convenience variable, but
Index: gdb-6.8cvs20080219/gdb/linux-nat.c
===================================================================
--- gdb-6.8cvs20080219.orig/gdb/linux-nat.c 2008-02-24 19:36:26.000000000 +0100
+++ gdb-6.8cvs20080219/gdb/linux-nat.c 2008-02-24 19:45:01.000000000 +0100
@@ -89,6 +89,15 @@
#define PTRACE_GETSIGINFO 0x4202
#endif
+#define STRINGIFY_ARG(x) #x
+#define STRINGIFY(x) STRINGIFY_ARG (x)
+
+static int linux_ptrace_post_attach (ptid_t ptid, int *cloned_return);
+static int kill_lwp (int lwpid, int signo);
+
+/* PID of the inferior stopped by SIGSTOP before attaching (or zero). */
+static pid_t pid_was_stopped;
+
/* The single-threaded native GNU/Linux target_ops. We save a pointer for
the use of the multi-threaded target. */
static struct target_ops *linux_ops;
@@ -539,6 +548,11 @@ linux_child_follow_fork (struct target_o
}
else
{
+ /* We should check PID_WAS_STOPPED and detach it stopped accordingly.
+ In this point of code it cannot be 1 as we would not get FORK
+ executed without CONTINUE first which resets PID_WAS_STOPPED.
+ We would have to first TARGET_STOP and WAITPID it as with running
+ inferior PTRACE_DETACH, SIGSTOP will ignore the signal. */
target_detach (NULL, 0);
}
@@ -942,9 +956,8 @@ lin_lwp_attach_lwp (ptid_t ptid)
to happen. */
if (GET_LWP (ptid) != GET_PID (ptid) && lp == NULL)
{
- pid_t pid;
int status;
- int cloned = 0;
+ int cloned;
if (ptrace (PTRACE_ATTACH, GET_LWP (ptid), 0, 0) < 0)
{
@@ -958,37 +971,20 @@ lin_lwp_attach_lwp (ptid_t ptid)
return -1;
}
- if (debug_linux_nat)
- fprintf_unfiltered (gdb_stdlog,
- "LLAL: PTRACE_ATTACH %s, 0, 0 (OK)\n",
- target_pid_to_str (ptid));
-
- pid = my_waitpid (GET_LWP (ptid), &status, 0);
- if (pid == -1 && errno == ECHILD)
- {
- /* Try again with __WCLONE to check cloned processes. */
- pid = my_waitpid (GET_LWP (ptid), &status, __WCLONE);
- cloned = 1;
+ status = linux_ptrace_post_attach (ptid, &cloned);
+ if (status != 0)
+ {
+ error (_("Thread %s exited: %s"), target_pid_to_str (ptid),
+ status_to_str (status));
}
- gdb_assert (pid == GET_LWP (ptid)
- && WIFSTOPPED (status) && WSTOPSIG (status));
-
- if (lp == NULL)
- lp = add_lwp (ptid);
+ /* ADD_LWP with TID only already after the WAITPID. */
+ lp = add_lwp (ptid);
lp->cloned = cloned;
- target_post_attach (pid);
+ target_post_attach (GET_LWP (ptid));
lp->stopped = 1;
-
- if (debug_linux_nat)
- {
- fprintf_unfiltered (gdb_stdlog,
- "LLAL: waitpid %s received %s\n",
- target_pid_to_str (ptid),
- status_to_str (status));
- }
}
else
{
@@ -998,44 +994,202 @@ lin_lwp_attach_lwp (ptid_t ptid)
threads. Note that this won't have already been done since
the main thread will have, we assume, been stopped by an
attach from a different layer. */
- if (lp == NULL)
- lp = add_lwp (ptid);
lp->stopped = 1;
}
return 0;
}
+/* Detect `T (stopped)' in `/proc/PID/status'.
+ Other states including `T (tracing stop)' are reported as false. */
+
+static int
+pid_is_stopped (pid_t pid)
+{
+ FILE *status_file;
+ char buf[100];
+ int retval = 0;
+
+ snprintf (buf, sizeof (buf), "/proc/%d/status", (int) pid);
+ status_file = fopen (buf, "r");
+ if (status_file != NULL)
+ {
+ int have_state = 0;
+
+ while (fgets (buf, sizeof (buf), status_file))
+ {
+ if (strncmp (buf, "State:", 6) == 0)
+ {
+ have_state = 1;
+ break;
+ }
+ }
+ if (have_state && strstr (buf, "T (stopped)") != NULL)
+ retval = 1;
+ fclose (status_file);
+ }
+ return retval;
+}
+
+/* Handle the processing after PTRACE_ATTACH, the first WAITPID -> SIGSTOP.
+ Returns STATUS if the thread has exited, 0 otherwise.
+ Sets PID_WAS_STOPPED if the process was originally stopped.
+ Sets LP->CLONED if the given LWP is not the thread leader.
+
+ Scenario for a standard unstopped inferior:
+ * `S (sleeping)' or `R (running)' or similiar states.
+ * PTRACE_ATTACH is called.
+ * `S (sleeping)' (or similiar) for some while.
+ * `T (tracing stop)'.
+ * WAITPID succeeds here returning SIGSTOP (signalled by PTRACE_ATTACH).
+
+ Scenario for a formerly stopped inferior:
+ * `T (stopped)'.
+ * PTRACE_ATTACH is called.
+ * `T (stopped)' would stay indefinitely
+ Note since this moment the `TracerPid' field gets filled
+ (by PTRACE_ATTACH), it is no longer just the common `T (stopped)' state.
+ * If no one did WAITPID since sending SIGSTOP our WAITPID would return
+ SIGSTOP. The state still would not turn to `T (tracing stop)'.
+ * Usually its original parent (before PTRACE_ATTACH was applied) already
+ did WAITPID. The original parent already received our SIGSTOP
+ sinalled by our PTRACE_ATTACH.
+ In this case our own WAITPID would hang. Therefore...
+ * ... we do artificial: tkill (SIGCONT);
+ `PTRACE_CONT, SIGSTOP' does not work in 100% cases as sometimes SIGSTOP
+ gets remembered by kernel during the first PTRACE_CONT later and we get
+ spurious SIGSTOP event. Expecting the signal may get delivered to
+ a different task of the thread group.
+ `kill_lwp (SIGSTOP)' has no effect in this moment (it is already stopped).
+ * WAITPID returns the artifical SIGCONT.
+ (The possibly pending SIGSTOP gets vanished by specifically SIGCONT.)
+ * State turns `T (tracing stop)'.
+ In this moment everything is almost fine but we need a workaround as final
+ `PTRACE_DETACH, SIGSTOP' would leave the process unstopped otherwise:
+ * tkill (SIGSTOP);
+ * `PTRACE_CONT, 0'
+ * WAITPID returns the artifical SIGSTOP.
+
+ With the pending (unwaited for) SIGSTOP the artifical signal effects are:
+ kill (SIGSTOP)
+ PTRACE_ATTACH
+ /-tkill (SIGCONT), WAITPID: SIGCONT, WAITPID: hang !
+ //-tkill (SIGCONT), WAITPID: SIGCONT, PTRACE_CONT (SIG_0), WAITPID: wait (OK)
+ \\-tkill (SIGALRM), WAITPID: SIGSTOP, WAITPID: hang !
+ \-tkill (SIGALRM), WAITPID: SIGSTOP, PTRACE_CONT (SIG_0), WAITPID: SIGALRM !
+ Therefore we signal artifical SIGCONT and stop waiting after its reception.
+
+ For the detection whether the process was formerly stopped we need to
+ read `/proc/PID/status'. `PTRACE_CONT, SIGSTOP' returns ESRCH
+ for `S (sleeping)' and succeeds for `T (stopped)' but it unfortunately
+ succeeds even for `T (tracing stop)'. Depending on PTRACE_CONT, SIGSTOP
+ success value for formerly stopped processes would mean a race condition
+ as we would get false stopped processes detection if we get too slow.
+
+ `waitid (..., WSTOPPED)' hangs the same way as WAITPID.
+
+ Signals get queued for WAITPID. PTRACE_ATTACH (or TKILL) enqueues SIGSTOP
+ there but WAITPID may return an already pending signal.
+ Redeliver it by PTRACE_CONT, SIGxxx as otherwise it would get lost.
+ Similiar processing is being done in this file by WAIT_LWP. */
+
+static int
+linux_ptrace_post_attach (ptid_t ptid, int *cloned_return)
+{
+ unsigned long sig;
+ int this_thread_was_stopped;
+ int cloned = 0;
+
+ if (debug_linux_nat)
+ fprintf_unfiltered (gdb_stdlog,
+ "LLAL: PTRACE_ATTACH %s, 0, 0 (OK)\n",
+ target_pid_to_str (ptid));
+
+ /* This code should not be run for the threads being attached after the first
+ thread (process) as we would get later spurious SIGCONT otherwise. */
+
+ this_thread_was_stopped = pid_is_stopped (GET_LWP (ptid));
+ if (this_thread_was_stopped)
+ {
+ pid_was_stopped = GET_PID (ptid);
+ if (kill_lwp (GET_LWP (ptid), SIGCONT) != 0)
+ perror_with_name (("kill_lwp (SIGCONT)"));
+ }
+
+ for (;;)
+ {
+ pid_t pid;
+ int status;
+
+ pid = my_waitpid (GET_LWP (ptid), &status, 0);
+ if (pid == -1 && errno == ECHILD)
+ {
+ /* Try again with __WCLONE to check cloned processes. */
+ pid = my_waitpid (GET_LWP (ptid), &status, __WCLONE);
+ cloned = 1;
+ }
+
+ gdb_assert (pid == GET_LWP (ptid));
+
+ if (debug_linux_nat)
+ {
+ fprintf_unfiltered (gdb_stdlog,
+ "LLAL: waitpid %s received %s\n",
+ target_pid_to_str (ptid),
+ status_to_str (status));
+ }
+
+ /* Check if the thread has exited. */
+ if (WIFEXITED (status) || WIFSIGNALED (status))
+ return status;
+ gdb_assert (WIFSTOPPED (status));
+ sig = WSTOPSIG (status);
+ gdb_assert (sig != 0);
+ if (sig == SIGSTOP)
+ break;
+
+ /* As the second signal for stopped processes we send SIGSTOP. */
+ if (this_thread_was_stopped && sig == SIGCONT)
+ sig = SIGSTOP;
+
+ printf_unfiltered (_("Redelivering pending %s.\n"),
+ target_signal_to_string (target_signal_from_host (sig)));
+ if (sig == SIGSTOP)
+ {
+ if (kill_lwp (GET_LWP (ptid), sig) != 0)
+ perror_with_name (("kill_lwp"));
+ /* We now must resume the inferior to get SIGSTOP delivered. */
+ sig = 0;
+ }
+ if (ptrace (PTRACE_CONT, GET_LWP (ptid), NULL, (void *) sig) != 0)
+ perror_with_name (("ptrace"));
+ }
+ *cloned_return = cloned;
+ return 0;
+}
+
static void
linux_nat_attach (char *args, int from_tty)
{
struct lwp_info *lp;
- pid_t pid;
int status;
- int cloned = 0;
+ int cloned;
/* FIXME: We should probably accept a list of process id's, and
attach all of them. */
linux_ops->to_attach (args, from_tty);
- /* Make sure the initial process is stopped. The user-level threads
- layer might want to poke around in the inferior, and that won't
- work if things haven't stabilized yet. */
- pid = my_waitpid (GET_PID (inferior_ptid), &status, 0);
- if (pid == -1 && errno == ECHILD)
- {
- warning (_("%s is a cloned process"), target_pid_to_str (inferior_ptid));
-
- /* Try again with __WCLONE to check cloned processes. */
- pid = my_waitpid (GET_PID (inferior_ptid), &status, __WCLONE);
- cloned = 1;
- }
-
- gdb_assert (pid == GET_PID (inferior_ptid)
- && WIFSTOPPED (status) && WSTOPSIG (status) == SIGSTOP);
-
/* Add the initial process as the first LWP to the list. */
inferior_ptid = BUILD_LWP (GET_PID (inferior_ptid), GET_PID (inferior_ptid));
+
+ status = linux_ptrace_post_attach (inferior_ptid, &cloned);
+ if (status != 0)
+ error (_("Program %s exited: %s\n"), target_pid_to_str (inferior_ptid),
+ status_to_str (status));
+ if (cloned)
+ warning (_("%s is a cloned process"), target_pid_to_str (inferior_ptid));
+
+ /* ADD_LWP with TID only already after the WAITPID. */
lp = add_lwp (inferior_ptid);
lp->cloned = cloned;
@@ -1046,8 +1200,8 @@ linux_nat_attach (char *args, int from_t
lp->resumed = 1;
if (debug_linux_nat)
{
- fprintf_unfiltered (gdb_stdlog,
- "LLA: waitpid %ld, faking SIGSTOP\n", (long) pid);
+ fprintf_unfiltered (gdb_stdlog, "LLA: waitpid %d, faking SIGSTOP\n",
+ GET_PID (inferior_ptid));
}
}
@@ -1092,6 +1246,9 @@ detach_callback (struct lwp_info *lp, vo
overall process id just yet. */
if (GET_LWP (lp->ptid) != GET_PID (lp->ptid))
{
+ /* None of these threads should be stopped for PID_WAS_STOPPED. Only the
+ last thread (process) will be stopped by LINUX_NAT_DETACH. */
+
errno = 0;
if (ptrace (PTRACE_DETACH, GET_LWP (lp->ptid), 0,
WSTOPSIG (lp->status)) < 0)
@@ -1120,6 +1277,9 @@ linux_nat_detach (char *args, int from_t
trap_ptid = null_ptid;
+ if (pid_was_stopped == GET_PID (lwp_list->ptid))
+ args = STRINGIFY (SIGSTOP);
+
/* Destroy LWP info; it's no longer valid. */
init_lwp_list ();
@@ -1255,6 +1415,14 @@ linux_nat_resume (ptid_t ptid, int step_
resume_callback. */
lp->stopped = 0;
+ /* At this point, we are going to resume the inferior and if we
+ have attached to a stopped process, we no longer should leave
+ it as stopped if the user detaches. PTID variable has PID set to LWP
+ while we need to check the real PID here. */
+
+ if (!step && lp && pid_was_stopped == GET_PID (lp->ptid))
+ pid_was_stopped = 0;
+
if (resume_all)
iterate_over_lwps (resume_callback, NULL);
Index: gdb-6.8cvs20080219/gdb/doc/gdb.texinfo
===================================================================
--- gdb-6.8cvs20080219.orig/gdb/doc/gdb.texinfo 2008-02-24 19:36:24.000000000 +0100
+++ gdb-6.8cvs20080219/gdb/doc/gdb.texinfo 2008-02-24 19:36:26.000000000 +0100
@@ -2176,16 +2176,29 @@ can step and continue; you can modify st
process continue running, you may use the @code{continue} command after
attaching @value{GDBN} to the process.
+For a process already being stopped before the @code{attach} command executed
+you get the informational message below. Other signals may be occasionally
+shown if they were being delivered right the time the @code{attach} command
+executed. Such process is left still stopped after the @code{detach} command
+as long as you have not used the @code{continue} command (or similiar one)
+during your debugging session.
+
+@smallexample
+Attaching to program: /bin/sleep, process 16289
+Redelivering pending Stopped (signal).
+@end smallexample
+
@table @code
@kindex detach
@item detach
When you have finished debugging the attached process, you can use the
-@code{detach} command to release it from @value{GDBN} control. Detaching
-the process continues its execution. After the @code{detach} command,
-that process and @value{GDBN} become completely independent once more, and you
-are ready to @code{attach} another process or start one with @code{run}.
-@code{detach} does not repeat if you press @key{RET} again after
-executing the command.
+@code{detach} command to release it from @value{GDBN} control. Detaching the
+process continues its execution unless it was already stopped before the
+attachment and a @code{continue} type command has not been executed. After the
+@code{detach} command, that process and @value{GDBN} become completely
+independent once more, and you are ready to @code{attach} another process or
+start one with @code{run}. @code{detach} does not repeat if you press
+@key{RET} again after executing the command.
@end table
If you exit @value{GDBN} while you have an attached process, you detach